The invention relates to a continuous direct application of decorative foils to particle boards and an apparatus for the preparation of the particle board surfaces therefor.
Since the late seventies particle boards are manufactured by double band presses in a continuous process. This resulted in advantages with regard to quality and efficiency. Similar advances in the processing of particle boards have not been achieved since then.
Before application of the foils the particle board surfaces must be roughened. For the roughening of the particle board surfaces, wide-band grinding machines are still in use. During the manufacture of particle boards in non-continuous multilayer plate presses, a so-called sand layer is formed in which the resin is cured too early and which is therefore brittle. It has to be removed from the particle board before further processing so that a decorative coating can be firmly attached to the surface.
The improved process procedure in double band presses prevents the formation of such sand layers. Instead, a so-called press skin is formed which is a thin surface layer consisting essentially exclusively of resin. This surface is very smooth and is accordingly not a suitable base for cove rings which are cemented thereon or directly applied thereto. It has to be slightly toughened in order to provide for an excellent adhesion base.
Band grinding machines are not capable of simply roughening the press skin. They remove generally several tenths of a millimeter of material if increasingly dull grinding particles are present on the surface. This material then becomes lost as grinding dust and generates problems with regard to work safety and the environment. Since further the grinding equipment has a particular geometrical shape, such shape is transferred to the particle board surface. However the shapes of the press surfaces of a band grinding machine are generally less accurate than those of the double band press so that thickness errors are ground into the particle board surface.
In addition the band grinding machines produce, depending on the arrangement, longitudinal or transverse grooves in the particle board surface which, under disadvantageous circumstances, may show on the surface of the subsequently applied coating layer.